1. Field of the Invention
The present invention relates to a photoresist composition, a preparation method thereof and a method for forming a pattern during semiconductor processing using the composition. More particularly, the invention relates to a positive photoresist composition which has a high sensitivity and a high resolution for producing patterns having an excellent profile.
2. Description of Related Art
Recently, due to the wide-spread usage of computers in fast developing information media, there is a prevalent need for a semiconductor memory device having a high speed and a large operating storage capacity. Methods for manufacturing semiconductor memory devices currently are being developed to improve the degree of integration, the reliability and the response time. Particularly, the development of photolithography is now important as a critical technique for increasing the degree of integration of the memory devices.
Developments in increasing the degree of integration currently are ongoing. For example, DRAM (dynamic random access memory) devices such as 16 Mbit DRAM and 64 Mbit DRAM, now are mass-produced, and a 256 Mbit DRAM device is under development for mass-production. In addition, mass-producing Giga bit DRAM devices also are currently under development.
As these highly integrated semiconductor devices are being produced, the factors involved in the photolithography process that typically is utilized during manufacture of these devices, are more and more strictly controlled. In particular, the specific photoresist composition that is used for the photoresist process is a basic underlying factor in developing these semiconductor devices. Hence, the requirements for the quality of the photoresist increase every year.
A conventional method for forming a pattern utilizing the photolithography process employing a common photoresist composition can be described as follows. First, a photoresist layer, which usually is an organic layer whose solubility with respect to an alkali-solution changes by exposure to light, such as ultraviolet or X-ray, is coated on a substrate on which a layer to be patterned, such as a dielectric layer or a conductive layer, will be formed. On the photoresist layer, a mask having a predetermined pattern to selectively expose a predetermined portion of the photoresist layer is positioned and the photoresist layer is exposed to light through the mask. Then, the portion having a high solubility (the exposed portion for a positive photoresist) typically is removed by using a developing solution (typically referred to as development) and the portion having a low solubility remains, to thereby produce a photoresist pattern. The portions of the substrate now exposed by the photoresist pattern then can be etched to form a pattern in the substrate, and then the remaining photoresist removed to obtain a desired pattern for wiring and forming an electrode.
As a light source for the exposure, light having a G-line wavelength (436 nm) is widely used as the ultraviolet. However, light having a shorter I-line wavelength (365 nm) is preferred when considering resolution and depth of focus. As will be appreciated by those skilled in the art, the components of the photoresist composition vary depending on the particular light source.
Typical photosensitive materials employed in a photoresist composition include compounds such as ester compounds of polyhydroxy benzophenone, naphthoquinone diazide-5-sulfonic acid, and the like. Particularly, ester compounds of 2,3,4,4xe2x80x2-tetrahydroxy benzophenone are widely utilized (See Shoji Kawata, Motofumi Kashiwagi, et al., Journal of Polymer Science and Technology, Vol. 4, No. 1 pp. 101-108 (1991)). However, this compound has a lack of transparency for light having an I-line wavelength. As a result, it absorbs light having an I-line wavelength after the exposure, and the profile and resolution of the thus obtained photoresist pattern utilizing an I-line light source is unsatisfactory.
Photoresist compositions including a novolak resin of cresol-formaldehyde, along with a naphthoquinone diazide-substituted photosensitive material, are disclosed in U.S. Pat. Nos. 3,046,118, 3,106,465, 3,148,983, 4,115,128 and 4,173,470, and in Japanese Patent Laid-open Publication No. Sho 62-28457. Typical photoresist compositions including novolak resins and trihydroxy benzophenone-1,2-naphthoquinone diazide sulfonic acid ester are disclosed in L. F. Thompson, xe2x80x9cIntroduction to Microlithography,xe2x80x9d ACS Publishing Co. Ltd., No. 219 pp.112-121. In addition, U.S. Pat. No. 5,648,194 discloses photoresist compositions containing alkali-soluble resins, o-naphthoquinone diazide sulfonic acid ester, and vinyl ether, and U.S. Pat. No. 5,468,590 discloses photoresist compositions containing alkali-soluble resins prepared by using quinone diazide compounds and polyphenol. Photoresist compositions having improved physical characteristic which also include novolak resins, quinone diazide compounds and polyphenol are disclosed in U.S. Pat. No. 5,413,895.
As described above, compounds having the naphthoquinone diazide function can be used for the photosensitive material and among them, naphthoquinone diazide-5-sulfonic acid ester, naphthoquinone diazide-4-sulfonic acid ester, and the like are particularly preferred (See J. Kosar, LIGHTSENSITIVE SYSTEMS, John Wiley and Sons Inc. pp.343-361). U.S. Pat. No. 5,714,620 discloses positive photoresist compositions including a quinone diazide sulfonate compound of polyphenol.
To increase the ability of the photosensitive naphthoquinone diazide function to accomplish a high resolution, a method for using a photosensitive material having a large amount of triester groups is disclosed in Japanese Patent Laid-open Publication No. Sho 60-158440. Further, a method for adding an organic solvent having a solubility parameter of 11-12 is disclosed in Japanese Patent Laid-open Publication No. Sho 61-260239. However, since a solvent such as dimethyl sulfoxide is used, the photoresist composition containing the solvent is unstable during storage, and the sensitivity and resolution of the composition is remarkably lowered during extended storage.
Japanese Patent Laid-open Publication No. Hei 1-189644 discloses positive photoresist compositions including a photosensitive group having a specific tris(hydroxyphenyl) methane compound as a base, instead of a naphthoquinone-1,2-diazide sulfonic acid ester of polyhydroxy benzophenone. However, the heat-resistance of this photoresist composition is lower than that of polyhydroxy benzophenone-based composition and the photosensitive group is liable to precipitate, thereby decreasing its storage stability.
Various compounds having phenolic hydroxy groups are known to be useful as photosensitive materials. However, various characteristics such as the sensitivity, resolution, heat-resistance, and the like cannot be satisfied simultaneously. Efforts on improving the physical characteristics by mixing photosensitive compounds having different characteristics have been implemented. For example, U.S. Pat. No. 5,378,586 discloses photoresist compositions having an improved resolution which includes a photosensitive compound that is obtained by mixing diazide-based sulfonic acid esters having different characteristics.
In order to improve the sensitivity, the amount of the photosensitive material in the photoresist should be decreased. This, however, typically will lower the resolution. In order to improve the resolution, the hydrophobicity of the novolak resin should be increased. This, however, typically lowers the sensitivity. As a result, it is difficult to obtain a composition that satisfies both conditions; sensitivity and resolution.
Hence, there is a need to develop a photoresist composition that can achieve both a high sensitivity and a high resolution simultaneously. In addition, there is a need to develop a single photoresist composition that can be exposed to lights having a G-line wavelength and an I-line wavelength in order to obtain a photoresist pattern having a good profile and resolution during the manufacture of a semiconductor device. Particularly, there is a need to provide a photoresist composition that can be exposed to light having an I-line wavelength to thereby yield a good pattern profile in a more largely integrated device.
It is therefore a feature of the present invention to satisfy these needs by providing a photoresist composition that has improved characteristics, such as improved resolution, heat-resistance, residual ratio, and sensitivity, and that can commonly be applied during the manufacturing process of semiconductor devices. Another feature of the present invention is to provide a suitable method for preparing the positive photoresist composition. A further feature of the present invention is to provide a method for forming patterns having an improved profile by utilizing the above-mentioned photoresist composition.
To accomplish these and other features of the present invention, there is provided a photoresist composition comprising: (i) a photosensitive material obtained by mixing about 30-70% by weight of a first photosensitive compound represented by formula (1) with about 70-30% by weight of a second photosensitive compound represented by formulae (2a) or (2b); (ii) a resin; and (iii) a solvent 
wherein in formula (1), R1 and R2 are independently selected from the group consisting of a hydrogen atom, a 1,2-naphthoquinone diazide-4-sulfonyl group, a 1,2-naphthoquinone diazide-5-sulfonyl group, a 1,2-naphthoquinone diazide-6-sulfonyl group, and mixtures thereof, and R1 and R2 cannot be a hydrogen atom at the same time, n1 and n2 represent 0, 1, 2 or 3 and cannot be 0 at the same time, and
wherein in formulae (2a) and (2b), R3, R4 and R5 are independently selected from the group consisting of a hydrogen atom, a 1,2-naphthoquinone diazide-4-sulfonyl group, a 1,2-naphthoquinone diazide-5-sulfonyl group, a 1,2-naphthoquinone diazide-6-sulfonyl group, and mixtures thereof, and R3, R4 and R5 cannot be a hydrogen atom at the same time, X1a, X1b, X1c, X1d, X2a, X2b and X2c are independently selected from a hydrogen atom or an alkyl group, and n3 represents 1 or 2.
An additional feature of the present invention can be accomplished by providing a method for making a photoresist composition comprising:
preparing a first photosensitive compound represented by formula (1) by implementing an esterification reaction between a polyol compound represented by formula (1xe2x80x2) and at least one compound selected from the group consisting of 1,2-naphthoquinone diazide-4-sulfonyl chloride, 1,2-naphthoquinone diazide-5-sulfonyl chloride, and 1,2-naphthoquinone diazide-6-sulfonyl chloride;
preparing a second photosensitive compound represented by formulae (2a) or (2b) by implementing an esterification reaction between a polyol compound represented by formulae (2axe2x80x2) or (2bxe2x80x2) and at least one compound selected from the group consisting of 1,2-naphthoquinone diazide-4-sulfonyl chloride, 1,2-naphthoquinone diazide-5-sulfonyl chloride, and 1,2-naphthoquinone diazide-6-sulfonyl chloride;
preparing a photosensitive material by mixing about 30 to about 70% by weight of the first photosensitive compound and about 70 to about 30% by weight of the second photosensitive compound; and
dissolving the photosensitive material and a resin in a solvent 
wherein in formulae (1) and (1xe2x80x2), R1 and R2 are independently selected from the group consisting of a hydrogen atom, a 1,2-naphthoquinone diazide-4-sulfonyl group, a 1,2-naphthoquinone diazide-5-sulfonyl group, a 1,2-naphthoquinone diazide-6-sulfonyl group, and mixtures thereof, and R1 and R2 cannot be a hydrogen atom at the same time, n1 and n2 represent 0, 1, 2 or 3, and cannot be 0 at the same time; and
wherein in formulae (2a), (2axe2x80x2), (2b) and (2bxe2x80x2), R3, R4 and R5 are independently selected from the group consisting of a hydrogen atom, a 1,2-naphthoquinone diazide-4-sulfonyl group, a 1,2-naphthoquinone diazide-5-sulfonyl group, a 1,2-naphthoquinone diazide-6-sulfonyl group, and mixtures thereof, and R3, R4 and R5 cannot be a hydrogen atom at the same time, X1a, X1b, X1c, X1d, X2a, X2b and X2c are independently selected from a hydrogen atom or an alkyl group, and n3 represents 1 or 2.
To accomplish an additional feature of the present invention, there is provided a method for forming a pattern comprising:
providing a substrate;
forming a photoresist layer on a substrate by coating a photoresist composition including: (i) a photosensitive material obtained by mixing about 30 to about 70% by weight of a first photosensitive compound represented by formula (1) and about 70 to about 30% by weight of a second photosensitive compound represented by formulae (2a) or (2b); (ii) a resin; and (iii) a solvent;
exposing the photoresist layer utilizing a light source; and
forming a photoresist pattern by developing the exposed photoresist layer 
wherein in formula (1), R1 and R2 are independently selected from the group consisting of a hydrogen atom, a 1,2-naphthoquinone diazide-4-sulfonyl group, a 1,2-naphthoquinone diazide-5-sulfonyl group, a 1,2-naphthoquinone diazide-6-sulfonyl group, and mixtures thereof, and R1 and R2 cannot be a hydrogen atom at the same time, n1 and n2 represent 0, 1, 2 or 3 and cannot be 0 at the same time, and
wherein in formulae (2a) and (2b), R3, R4 and R5 are independently selected from the group consisting of a hydrogen atom, a 1,2-naphthoquinone diazide-4-sulfonyl group, a 1,2-naphthoquinone diazide-5-sulfonyl group, a 1,2-naphthoquinone diazide-6-sulfonyl group, and mixtures thereof, and R3, R4 is and R5 cannot be a hydrogen atom at the same time, X1a, X1b, X1c, X1d, X2a, X2b and X2c are independently selected from a hydrogen atom or an alkyl group, and n3 represents 1 or 2.